| Soil moisture affects the partitioning of radiative energy into latent and sensible heat fluxes and therefore moist convection and the planetary boundary layer,and height of the lifting condensation level,thereby affects the occurrence of precipitation.Studying the effect of soil moisture on precipitation not only helps to understand the process of energy and water exchange between land and atmosphere and improves the initial field of model,but also improves the ability to predict precipitation.Firstly,the temporal and spatial distribution characteristics of soil moisture and precipitation in China and its surrounding areas were analyzed.Secondly,based on the intermediate process of soil moisture affecting precipitation,soil moisture-precipitation coupling in China and its surrounding areas was quantified by dividing it into land segment and atmospheric segment.Finally,the WRF model is applied to analyze a heavy rainfall that occurred in the strong coupling zone and discussed the impact of the land surface process plans and soil moisture.The main results are as follows:?1?By dividing China and its surrounding areas into three regions:northern,southern and central regions,the temporal and spatial distribution characteristics of summer precipitation and soil moisture in each region during 1981-2008 were analyzed.The results showed that both the precipitation and soil moisture in China and its surrounding areas were the largest in the southern region,followed by the northern region and the smallest in the central region.From 1981 to 2008,the soil moisture in central and northern regions showed a downward trend,and remained flat in the southern region,while the precipitation in all three regions showed a downward trend,which may be associated with global warming.?2?The soil moisture-latent heat flux coupling index(ILH)and the latent heat flux-lifting condensation level coupling index(ILCL)were used to quantify the coupling intensity of soil moisture and precipitation in China and its surrounding areas in summer.The results showed that in the North China Plain,the Northeast Plain,and central Mongolia,ILH and negative ILCL are relatively large,therefore,the soil moisture-precipitation coupling is strong in these areas.In the central Qinghai-Tibet Plateau and the Deccan Plateau in India,both ILH and negative ILCL are small,therefore the soil moisture and precipitation coupling is weak in these areas.The latent heat flux plays a very important role in the soil moisture-precipitation coupling,the reason for the weak coupling may be that the latent heat flux is small and its spatial variation is not obvious.?3?Using four different land-surface processes:the heat diffusion scheme,the Noah land surface scheme,the LSM land surface scheme and the urban canopy scheme,an afternoon heavy rainfall process in the area with strong soil moisture-precipitation coupling?Liaocheng,Shandong?was analyzed.The circulation situation analysis showed that the heavy rainfall was caused by many factors.High altitude trough and ridge brought cold air over Liaocheng and its surrounding areas,while the low-level jet delivered warm and moist air below the dry and cold air,besides,the air temperature in the near-surface layer was warmer with the higher ground temperature in the afternoon,thus formed the convective unstable stratification.In addition,surface evaporation prospered in the afternoon,the relatively low pressure formed by the evaporation of surface combined with the high-altitude trough over liaocheng,caused warm and humid air currents to converge and rise,leading to the occurrence of the heavy rainfall.The results of numerical simulation and sensitivity tests showed that the configuration of low-altitude convergence and high-altitude divergence was the main factors for the occurrence of the heavy rainfall.Both latent heat flux and precipitation are sensitive to soil moisture,increasing?decreasing?soil moisture will increase?decrease?latent heat flux and precipitation. |
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